Spark plug



T. DUKELOW Nov. s; 1938.

SPARK PLUG Filed May 15, 1957 jive/afar;- f'fiarrzas DuXeZaw;

may;

Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE 2 Claims.

My invention relates to spark plugs for internal combustion engines and the like.

An object of my invention is to providea simple, practical, economical and efiicient device 5 of the character described.

Another object is to provide a spark plug having greatly improved operating characteristics in which is provided two gaps for the sparking feature. 10 Other objects and advantages will appear and be brought out more fully from the following specification, reference being had to the accompanying drawing wherein:

Fig. 1 is a side view of a spark plug embodying 15 my invention;

Fig. 2 is a similar view partly in central section;

Fig. 3 is a bottom view of the same; and Figs. 4 and 5 are respectively views in section 20 of the inner insulator and electrode. Referring more particularly to the drawing, I show a spark plug ll) of the conventional type having a metallic shell ll. provided with a cylindrical bore I2, a reduced bore l3, the'bores l2 and I3 being merged in a shoulder H, the bore I! having alower edge portion IS in which is provided the usual terminal stud IS. The shell i I is further provided with an internally threaded portion l1 and an externally threaded portion l8. The plug is provided with the usual porcelain dielectric l9 having an internal bore 20 for the iniulated electrode 2| and is further provided with a cylindrical portion 22 adapted to fit into bore l2 and has the usual tip protecting extension 23 beyond which extends the tip 24 of the electrode 2!. A shoulder 25 is formed on dielectric l9 and is adapted to provide a seat for a gasket 26 held in place by bushing 21. The electrode 2| has the usual terminal bolt 28,

40 and a bushing 29 made of any suitable insulating material is located in bore l3 andhas an internal bore illyan enlarged bore 3|, a shoulder 92, an abutment surface 33 and anouter cylindrical portion 34 from which construction it will be apparent that the'bu'shing 29 is retained in the shell II by the downward pressure of the cylindrical portion 22 of the dielectric l9 against the ring 33, the shoulder ll of shell ll serving to position the bushing 29 in place. A metallic bushing 35 having an internal bore 39 adapted to receiveextcnsion 23 is provided with a shoulder 31 and has an outer cylindrical surface 38 adapted to fit into bore 39 of bushing 29. Bushing 35 is provided with an electrode 39 which 55 is positioned between the electrode l6 and tip 24 of electrode 2| and it will thus be apparent thatthe electrode 39 is located in the usual spark gap which is between electrode l6 and electrode tip 24.

The operation of the invention is believed to be obvious. The provision of the intermediate electrode 39 which is seen to be insulated both from the shell and the electrode 2| and in the normal spark. gap of the device it will be seen that two gaps are at once provided for the spark and the resulting operation is such that a much more eflicient or hotter spark is provided. Furthermore, upon the failure of either gap to function the remaining gap is certain to become opera'tive and thus the life is greatly extended and its efiiciency materially improved.

I spirit'of the invention. I, therefore, do not wish to be limited to the precise details of construction set forth, but desire to avail myself of such variations and modifications as come Within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A device of the character described comprising a' metallic shell having an electrode in a side portion thereof, a central electrode insulated from said shell and adapted to be connected to a source of potential and forming a spark gap with said first electrode, a single auxiliary electrode of uniform small diameter positioned entirely in said spark gap in spaced relation to said first and second electrodes, and a mounting for i said auxiliary electrode insulated from said first and second electrodes, said mounting including a bushing within, said shell.

2. A device of the character described com- 40 prising a metallic cylindrical shell having an electrode extending radially inwardly adjacent the cylindrical end thereof, a dielectric having a central bore and a cylindrical exterior .portion adapted to fit within said shell, an electrode in said dielectric having an end portion adjacent said first mentioned electrode, and a metallic cylindrical bushing in said shell and insulated therefrom and provided with a single auxiliary electrode of uniform small diameter having its end portion terminating between said first and second electrodes, said shell bushing and dielectric having correlated shoulders adapted for interfitting attachment. 5

' THOMAS DUELOW. 

